Aircraft configuration with improved aerodynamic performance

ABSTRACT

An aircraft ( 10 ), in particular a trainer aircraft with improved aerodynamic performance, having a configuration able to keep a directional stability and a very good aerodynamic behaviour even at very high angles of attack, where, traditional configurations prove themselves inefficient. In particular, this configuration foresees a forebody ( 52 ) with variable section, optimised for high angle of attack flights, a LEX vortex control device ( 72 ) at least one diverterless air intake ( 46 ), and a wing profile ( 18, 20 ) optimised in order to reduce the buffet effects typical of low aspect ratio wings with thin profile and variable camber. The aircraft ( 10 ) presents, finally, staggered tails ( 44  and  38 ), to optimise the aerodynamic performance.

This patent is referred to an aircraft configuration with highaerodynamic performance; in particular the aircraft according to thepatent is designed like a high performance trainer with secondaryoperational capabilities.

Many aircraft have to be easily flown and must have peculiar dynamiccharacteristics in accordance with the mission to be carried out.

Typical examples of the above include light aircraft for aerobatics,trainers and combat aircraft.

These aircraft often have to flight at a high angle of attack (the anglebetween the aircraft and wind speed direction at any time).

It is easy to understand that, under these flight conditions, theaircraft has to be very stable and easily controlled by the pilot, inorder to maintain a safe attitude during flight.

This stability is obtained using special automatic equipment able togenerate forces and moments to counterbalance undesirable flightattitudes.

While the aircraft stability along the pitch axis can be controlledoptimising the static margin and time-to-double amplitude, the presenceof lateral-directional instability (on “roll” and “yaw” axes) at highangles of attack can be difficult to control even using highlysophisticated Flight Control Systems.

It is therefore necessary to maximise the aircraft lateral-directionalstability up to high angles of attack in order to allow aircraftcontrol/agility and to avoid flight departures and spins.

Usually and in particular lately, attempt has been done by simplymodifying the fuselage aerodynamic shaping and other aircraft parts. Upto now those attempts have not lead to successful results.

In the frame of the requirements listed above, one of the goal of thispatent is, therefore, to avoid the mentioned problems and, inparticular, the problem relevant to an aircraft configuration withimproved aerodynamic performance, able to optimise the aircraftbehaviour especially during high angle of attack flights.

Another goal of this patent is to present an aircraft configuration withimproved aerodynamic performance, able to reduce buffet effects typicalof low aspect ratio wings with thin profile and variable camber.

Another goal of this patent is to realise an aircraft configuration withhigh aerodynamic performance, able to avoid successfully, the loss oflateral-directional stability and the negative effects generated by theengine flow next to the fuselage side wall and the horizontal tail, asfar as drag, stability and longitudinal control are concerned.

An additional goal of this patent is to realise an aircraftconfiguration with improved aerodynamic performance, able to recoverfrom spin, optimising, in general, the aircraft behaviour at high anglesof attack.

These and other goals are met by an aircraft configuration with improvedaerodynamic performance, according to claim 1, to which we refer to.

Profitably, the aircraft subject of this patent is designed, inparticular, like a trainer with high performance and secondaryoperational capabilities.

The configuration includes a twin engine “formula” and it ischaracterised by the presence of a range of very peculiar structuraldetails.

The twin-seat cabin (in tandem) with interconnected flight controls iscoupled with, a forebody with basically circular and variable section,characterised by low aspect ratio, optimised for high angles of attackflights. In this space a radar for the aircraft operational version canbe easily integrated.

The forebody shape and dimensions are optimised in order to reduce itsvortex interference on the aircraft aerodynamic characteristics atmid/high angles of attack; the mentioned characteristics allow to reducethe directional asymmetries at high angles of attack, typical offorebody with circular or elliptical section.

Moreover the wing profile is different from the standard wing profiles,in order to integrate a system able to minimise the buffet effects,typical of low aspect ratio wings with thin profile and variable camber.

The aerodynamic design includes also a LEX (Leading Edge Extension)vortex control device, properly sized, in order to symmetrize the LEXvortex bursting at mid/high angles of attack, as the symmetric vortexbursting allows to keep the lateral-directional stability and theaircraft control at mid/high angles of attack.

The training aircraft under this patent has, at least one engine airintake able to guarantee the performance and a proper fluid-dynamicinterface with the engine; the design does not foresee the integrationof a typical diverter on the upper lip of an air intake, integrated witha LEX.

Finally, the horizontal tail staggering allows to get a decrease in theaerodynamic drag produced by the fuselage afterbody, to optimise theaircraft spin behaviour and to improve the aircraft aerodynamic designfor high angles of attack manoeuvres.

Further goals and benefits of this patent shall be clear from thefollowing description and from the attached drawings, provided solely,but not limited to a sample, as follows:

-   -   picture 1 is a side view of an aircraft., in particular of a        trainer aircraft, designed accordingly this patent;    -   picture 2 is a top view of an aircraft, in particular of a        trainer aircraft, designed accordingly to this patent;    -   picture 3 is a bottom view of an aircraft, in particular of a        trainer aircraft, designed accordingly to this patent;    -   picture 4 is a front view of an aircraft, in particular of a        trainer aircraft, designed accordingly to this patent;    -   picture 5 is a back side view of an aircraft, in particular of a        trainer aircraft, designed accordingly to this patent;    -   picture 6 is a section, along the VI-VI line of picture 2;    -   picture 7 is a partial and enlarged view of a detail of the        aircraft configuration designed accordingly to this patent;    -   picture 8 is a section, along the VIII-VIII line of picture 7;    -   picture 9 is a section, along IX-IX line of picture 7;    -   picture 10 is a section, along X-X line of picture 7;    -   picture 11 is a section, along XI-XI line of picture 7;    -   picture 12 is a section, along XII-XII line of picture 7;    -   picture 13 is a section, along XIII-XIII line of picture 7;    -   picture 14 is a section, along XIV-XIV line of picture 7;    -   picture 15 is a section, along XV-XV line of picture 7;    -   picture 16 is a section, along XVI-XVI line of picture 7;    -   picture 17 is a section, along XVII-XVII line of picture 7;    -   picture 18 is an enlarged isoview of a detail of the aircraft        configuration designed accordingly to this patent.

Making reference to the mentioned pictures, an aircraft, in particular atrainer aircraft, having a configuration with improved aerodynamicperformance, accordingly to this patent, is generally indicated withreference 10.

The aircraft 10 includes a fuselage 12, having an upper side wall 14 anda lower side wall 16, and two wings, respectively a right wing 18 and aleft wing 20, fitted to the fuselage 12.

The right wing 18 has the tip 22, while the left wing 20 has the tip 24.

The aircraft 10 features also a rudder 34, fitted to the vertical fin 38and a horizontal stabiliser 44 having a right horizontal stabiliser 26and a left horizontal stabiliser 28 and relevant tips 30, 32.

In preferred or realising, but not limiting forms of the patent, asalready mentioned above, the type configuration is a twin-engine formulaand foresees two air intakes 46 for the engines 48, with relative enginenozzles 60.

Finally, in the fuselage forebody area 52, in which a radar for theaircraft 10 operational version could be integrated, a two in tandempilot cockpit 54 is installed, with interconnected flight controls,protected by a windshield 62. A probe 58 could be foreseen, in order tocarry out in flight refuelling for the aircraft 10.

With reference to pictures 2 and 3, each wing 18, 20 of the aircraft 10presents outer ailerons 56 and take-off and landing double slotted flaps64, integrated in the trailing edge 70 of each wing 18, 20, and otherdevices for wing camber optimisation (leading edge droops) 66,integrated in the wing leading edge 68. Their profile is shapedfollowing a particular geometry, on the basis of the general aerodynamicdesign mentioned in this description.

In particular, the technical characteristics of the aircraft 10, aimedto obtain high aerodynamic performance and flight stability, accordingto this patent, are as follows.

First of all, the aerodynamic design is characterised by the presence ofa LVC (“LEX Vortex Controller”) device to control the LEX (“Leading EdgeExtension”) vortex at mid/high angles of attack (ref. 72, picture 1).

The LEX, with gothic platform equal to 6.4% of the reference wing grossarea (as per this patent), allows vortex lift generation at high anglesof attack and LEX design is further refined integrating the LVC (“LEXVortex Controller”) at its tip, in order to ensure the vortex symmetricbursting at high angles of attack for sideslip attitudes and preventloss of lateral-directional stability.

The LEX vortex controller sizing 72 depends on the front LEX size and,in any case, the bigger the LEX is the higher the LVC must be; thetolerance can be defined by the ratio between the LEX area and theheight of the corresponding LVC. The design point of this ratio is equalto 2.35 m and the applicable tolerance range varies from +100% and −50%from the design point.

The fuselage forebody 52 shape of the aircraft 10 and its dimensions areeven more optimised in order to reduce its vortex interference on theaerodynamic characteristics of the aircraft 10 at mid/high angles ofattack; the mentioned characteristics allow also to reduce thedirectional asymmetries at high angles of attack, typical for theforebody with standard circular or elliptical sections.

The forebody 52 of the aircraft 10, according to the patent, shows arange of forebody sections with different geometry starting from theapex 74 up to the forebody edge merging with the LEX apex.

An exemplifying and preferred, but not limiting way, of the geometricshape and of the sequence of sections with different geometry, betweenthe apex 74 and a section referred to the quote 76 (positioned more orless at the beginning of the twin-seat cabin 54), is presented, insequence, at pictures 8-17, from which is inferable that from a roughlylow aspect ratio circular section (pictures 8-11) a chined section isgot (pictures 12-17).

From the mentioned pictures is clear the shift of the forebody 52 fromthe longitudinal axis K, from the apex 74 up to the reference sectionpresented in picture 17. In particular, according to a preferred form ofthe patent, the ratio between the length of the forebody 52, startingfrom the apex 74 up to the section along the XVII-XVII line (referenceL), and the average between the lengths A and B of the two axes of thesection (section presented in picture 17), presents a value of 1,873,with a tolerance equal to ±10%.

The structural peculiarity and its effect on the flight conditions comeout from the combination of the parameter mentioned above (plus or minusthe tolerance, if any) and the sequence of the forebody 52 sections,from the apex 74 of the aircraft 10 up to the reference section alongXVII-XVII line.

In picture 18 is also shown in detail an engine air intake, indicated asitem 46, which contributes to guarantee the performance of aircraft 10,above all as far as the fluid-dynamic interface with the relevant jetengine is concerned.

The air intake 46 shows a variable leading edge radius optimised in thelower part in order to reduce the engine face flow distortion at highangles of attack and in the side part in order to reduce the transonicspillage drag.

In particular, the inner lip average leading edge radius 76A is equal to7 mm, while the lower lip average leading edge radius 78 is equal to17.5 mm and that of the outer lip 80 is equal to 14 mm, so that thecapture area of the air intake is about 0.322 m², and the throat area ofthe air intake is about 0.257 m² and the engine face area is about 0.273m² (this values are referred to one air intake).

The air intake 46 is diverteless on the upper side of each air intakeside and integrated with a LEX, thanks to the peculiar ratio between LEXlength and shape; effectively the LEX acts as a shield at high angles ofattack.

The air intake can foresee also the presence of two additional blowindoors (not showed in the pictures), positioned on the upper wing-bodyjunction between wing 18, 20 and fuselage 12, which open when thepressure in the duct is lower than pressure on the upper wing-bodyjunction, thanks to pre-loaded springs integrated in the blow indoorhinges.

These blow indoors aim is to reduce, when they open, the local angles ofattack on the air intake lips 46 at high angles of attack, reducing theair mass flow quantity passing through the above mentioned air intake46.

One of the characteristics that guarantee the high performance, thestability and the aerodynamic structure of the aircraft 10, is thestaggered tails 44 and 38. They allow to reduce the aerodynamic draggenerated by the fuselage afterbody, to optimise the spin behaviour ofthe aircraft 10 and to improve its whole aerodynamic design for highangles of attack flights.

The vertical fin with trapezoidal platform includes the rudder 34 and iscoupled to the wing. This means that the leading edge of the rudder,indicated as item 36 in picture 1, overlapping the trailing edges 70 ofeach wing 18, 20, in order to allow the recovery from the spin and tooptimise the behaviour of the aircraft 10 at high angles of attack.

The horizontal tail with trapezoidal platform, is moved by twoindependent actuators which allow its symmetric and asymmetricdeflection. The horizontal tail presents a hinge axis, indicated as item86 in picture 2, which is oriented, on the right and on the left, ofabout 7.5°, from a lateral axis 88, in order to optimise the hinge andthe inertial moments.

The staggered tails can be further characterised by a tolerance referredto the ratio between quote C, showed in picture 1 and defined as thedistance between the apex of the vertical fin root chord and the apex ofthe horizontal tail root chord 44, and the tail arm, equal to 4181 mm;it follows that the reference ratio given above is equal to 1932/4181mm=0.462, with an applicable tolerance equal to 10%.

Also the wing profile is modified and optimised in comparison withtraditional trainer aircraft, in order to reduce the “buffet” effect,considering the characteristics of a low aspect ratio wing with thinairfoil and variable camber.

According to the patent, on the contrary, a wing 18, 20 with trapezoidalplatform and mid aspect ratio (AR=4) is used, characterised by thepresence of a saw tooth (showed as S in picture 2) at 67.5% of the grosswing span; the modification, in comparison with standard wings, is firstof all related to the leading edge radius, showed as R in picture 6which was circular (prior art) and now becomes triangular, in order tooptimise the stagnation point position, in presence of the leading edge68 and of the “Leading Edge Droops” 66 deflected at mid angles ofattack.

As clearly results from picture 6, which shows an enlarged section alongVI-VI line of picture 2, each wing 18, 20 presents a variable camberprofile, both along the leading edge 66 (“Leading Edge Droop”) and alongthe trailing edge 70, near the ailerons 56. The ailerons are scheduledonly in transonic regime, to have a camber reduction in order to reducecompressibility effects.

Quantitatively, the design point of the chord percentage extension ofthe leading edge 68 is equal to 0.36%, with a tolerance between +0.5%and −0.2% from the nominal value, while the design point of the grosswing span at which the chord extension is applied, in comparison withthe standard solutions, is equal to 8.2%, with a tolerance between +10%and −5% from the nominal value.

Other characteristics of the aircraft 10 include the fuselage 12, which,in the afterbody 16, foresees the integration of the engine nozzles andthe presence of a fuselage tail, indicated as item 90 in picture 3.

Also the area near the engine nozzles is optimised in order to reducethe negative effects, in terms of drag and longitudinalstability/control, generated by the engine flow next to the fuselageside wall 12 and the horizontal tail 44.

The aircraft 10 features also a tricycle landing gear, including a noselanding gear and a main landing gear. The nose landing gear is a legstrut, with four doors closing the bay, and backside retraction.

The main landing gear has frontside retraction in order to allowfuselage belly loads installation.

The aircraft 10 under this patent fits an automatic flight controlsystem (“Fly By Wire”), digital quadruplex redundant, which allows tooptimise the performance and the flight qualities; the system allows toimprove the flight safety limiting, automatically, flight regimes, whichcould be uncomfortable to the pilot or could lead to lose control(“Carefree Handling”).

From the above description the characteristics of the aircraftconfiguration with improved aerodynamic performance, subject to thispatent, are resulting clear, such as its advantages.

It is also clear that several other modifications can be applied to thestructure of the aircraft in subject, without exceeding the noveltiesincluded in the concept of the patent. It is also clear that, inapplying the patent, materials, shapes and dimensions of the abovementioned details could vary in compliance with the requirements and thesame details could be replaced with other details having the sametechnical characteristics.

1. Configuration of an aircraft (10) with improved aerodynamicperformance, which allow to keep directional stability and a very goodaerodynamic behaviour at mid/high angles of attack. This aircraft (10)includes a fuselage (12) fitted with wings (18, 20), at least one airintake (46) and a fuselage forebody (52) with variable section. Thisaircraft (10) includes also a LEX vortex control device (72) at mid/highangles of attack and staggered tails (44 and 38), obtained by thecoupling of the vertical fin to the wing (18, 20), whose leading edges(36) overlap the trailing edges (70) of each wing (18, 20), in order tooptimise the aerodynamic performance.
 2. Configuration of an aircraft(10) as per claim 1, characterised by the fact that the mentionedfuselage forebody (52) with low aspect ratio, shows a profile withvariable geometry starting from the apex (74) up to the edge couplingthe mentioned forebody (52) to the LEX apex. This profile shows,starting from the apex (74), a roughly circular section and then, at theLEX apex, chined section.
 3. Configuration of an aircraft (10) as perclaim 1, characterised by the fact that the LEX vortex control device(72) is shaped such to symmetrize the bursting of the vortex generatedby such LEX at mid-high angles of attack, in order to keep the stabilityand control of the aircraft (10)., avoiding lateral-directionalinstability.
 4. Configuration of an aircraft (10) as per claim 1,characterised by the fact that the staggered tails (44 and 38) is gotcoupling the vertical fin with trapezoidal platform to the wing (18, 20)and whose leading edges (36) overlap the trailing edges (70) of eachwing (18, 20), in order to optimise the behaviour of the aircraft (10)at high angles of attack.
 5. Configuration of an aircraft (10) as perclaim 4, characterised by the fact that such tail staggering is gotthrough a horizontal tail (44) having trapezoidal platform and thecapability of symmetric and asymmetric deflection. The horizontal tailpresents a hinge axis (86), which is inclined from a lateral axis (88)of the aircraft (10), in order to optimise the hinge and inertialmoments.
 6. Configuration of an aircraft (10) as per claim 1,characterised by the fact that the air intake (46) is diverterless onthe upper lip of the air intake.
 7. Configuration of an aircraft (10) asper claim 1, characterised by the fact that the air intake (46) shows ainner lip average leading edge radius (76A) equal to 7 mm, while thelower lip average leading edge radius (78) is equal to 17.5 mm and thatof the average outer lip (80) is equal to 14 mm, so that the capturearea of the air intake (46) is about 0.322 m², the throat area of theair intake (46) is about 0.257 m² and the engine face area is about0.273 m².
 8. Configuration of an aircraft (10) as per claim 1,characterised by the fact that additional blow indoors may be foreseen,positioned near the junction between at least one of the mentioned wings(18, 20) and the mentioned fuselage (12). The blow indoors open when thepressure inside engine ducts is lower than the pressure on the mentionedwing-body junction, reducing the local angles of attack and the quantityof air passing through the air intake (46).
 9. Configuration of anaircraft (10) as per claim 1, characterised by the fact that each wing(18, 20) of the aircraft (10) shows trapezoidal platform and at leastone saw tooth area (S) in at least one part of the wing span. This wing(18, 20) shows also a leading edge (68) and radius (R) with triangularprofile.
 10. Configuration of an aircraft (10) as per claim 1,characterised by the fact that each wing (18, 20) of the aircraft (10)shows a variable camber profile, both on the leading edge (66) and onthe trailing edge (70), in order to optimise camber profile improvingcompressibility effects.
 11. Configuration of an aircraft (10) withimproved aerodynamic performance as described and claimed and for thespecified goals.